Numerous approaches have been utilized in the optical industry to make micro-lens arrays. Some conventional approaches have included an ink-jet process to deposit ultraviolet curable lens material on a base element, a hot embossing process to manufacture polycarbonate lenses, or a resist reflow process to pattern a spherical surface. Each of these conventional approaches has a disadvantage. For example, using an ink-jet process creates difficulty in tailoring the surface shape of the lens element. While spherical lenses may be easily formed through an ink-jet process, control of such a process is difficult for asymmetrically shaped lenses. Hot embossing causes significant material shrinkage after the embossing, which may lead to distorted reproduction. Using resist reflow is expensive and requires the use of clean room facilities.
Upon preparation of a master micro-lens array, replica lens arrays may be formed through molding techniques which are well known in the optical industry. See, for example, U.S. Pat. No. 6,300,464 (Morijiri et al.), U.S. Pat. No. 6,301,055 (Legrand et al.), and U.S. Pat. No. 6,129,866 (Hamanaka et al). Conventional replication approaches, however, have failed to address various issues necessary to be solved before the formed replicas can be used in a commercial product. Some important issues include control of distortion of the mold, material loss, environmental stability, and refractive index tailoring of the optical elements.
There exists a need for a low cost micro-lens array which addresses one or more of the disadvantages found in conventional approaches.